1. Field of the Invention
The present invention relates generally to a closure for a container and particularly to a closure with means for indicating that the closure has been opened at least once.
2. Description of the Related Technology
There is an increasing demand for tamper-indicating systems which ensure that a container is not re-filled with non-original contents. Whilst it is relatively easy to produce some form of tamper-evidence, it is much more difficult to provide tamper-evidence which cannot be either overcome without causing the tamper-evidence system to activate, or activated and then returned to a visually identical state so as to appear non-activated.
A particularly useful method of providing tamper-evidence is to use a system in which a closure is initially located in a first position, but once removed can only be returned to a second position which is visually distinct from the first position. For example, U.S. Pat. No. 5,738,231 describes a closure with a part which is moved during the opening process so that following opening it cannot pass back over a projection on the container finish. The result is that the closure can only return to a position in which it is axially displaced with respect to its original position. Document WO 02/096771 describes a closure with a first portion with inner and outer parts, and a second portion. Initially a section of the inner part of the first portion protrudes below the level of the outer part and is held firmly by a region of the second portion which is formed so as to have a reduced circumference. When the first portion is removed the section of the inner part is pulled from under the area of reduced circumference on the second portion. After removal the inner part of the first portion and the area of reduced circumference on the second portion retain their original dimensions, so that if the first portion is reapplied the inner part can no longer pass under the area of reduced circumference. Accordingly a gap is produced between the outer part of the first portion and the second portion, because the section of the inner part which is previously trapped under the second portion is now trapped above the area of reduced circumference.
In both of the above prior art documents a gap is formed by trapping an obstructing member. The problem with such systems is that the obstruction member is easily accessible and could be removed, for example by cutting to defeat the tamper-evidence.